This invention relates to a swash-plate compressor for use in an automotive air conditioner or the like.
A swash-plate compressor of the type is disclosed, for example, in Japanese Patent Application Publications (JP-A) Nos. 2001-165041 and 2001-165046. The swash-plate compressor comprises a piston reciprocally moved by rotation of a swash plate fixed to a drive shaft. The swash plate and a coupling portion of the piston are slidably connected through a pair of semi-spherical shoes. Each of the shoes has a spherical surface which slides along a generally spherical contact surface of the coupling portion of the piston to thereby convert the rotation of the swash plate into reciprocal movement of the piston. The slidability and the seizure resistance between the spherical surface of the shoe and the contact surface of the coupling portion are important in order to assure the operability and the durability of the compressor as a whole.
Generally, one of the spherical surface of the shoe and the contact surface of the coupling portion along which the spherical surface of the shoe slides and moves is plated with Sn excellent in self lubrication or applied with a solid lubricant. Thus, a soft surface treatment layer having a lubricity is produced. With this structure, an excellent slidablity and an excellent seizure resistance are expected in an initial state.
However, because the surface treatment layer is soft, the surface treatment layer is easily peeled off or worn. Therefore, during long-time use, the wear resistance and the seizure resistance are not maintained. Furthermore, a lubricating oil between the contact surface of the coupling portion and the spherical surface of the shoe may be washed away by a condensed liquid refrigerant. If the compressor is started in the state where the contact surface and the spherical surface are dried up after the lubricating oil is washed away, the slidability of the shoe is further deteriorated. In addition, a high-load operation owing to liquid compression may bring about instantaneous wear or peeling-off of the surface treatment layer. This results in occurrence of scuffing on the contact surface and a risk of undesirably locking the compressor. In case where a natural refrigerant gas (for example, CO2, CH4) is used, it is supposed that a sliding portion of the compressor is required to have more strict environment adaptation. Therefore, it is desired to further improve the slidability and the seizure resistance.